Controlling device for a heat-dissipating system

ABSTRACT

A controlling device for a heat-dissipating system is provided to prevent a signal output by an external device electrically connected with the heat-dissipating system from being interfered with a pulse width modulation (PWM) signal used for controlling the voltage supply of the heat-dissipating system. The controlling device includes a signal generator, electrically connected between the heat-dissipating system and a power source supplying a voltage for the heat-dissipating system, for generating a control signal or a PWM signal for switching on/off the power source, and a voltage regulator electrically connected between the heat-dissipating system and the power source and connected in parallel with the signal generator for continuously providing the heat-dissipating system with a basic voltage so as to prevent that an output signal from the external device electrically connected with the heat-dissipating system is interfered with the control signal.

FIELD OF THE INVENTION

[0001] The present invention is related to a controlling device for a heat-dissipating system and especially to a pulse width modulation (PWM) control circuit for a direct-current (DC) fan.

BACKGROUND OF THE INVENTION

[0002] Please refer to FIG. 1 showing a conventional circuit for controlling the rotation speed of a fan 11 using a transistor 12 as a switch, wherein whether the voltage supply Vcc of DC fan is switched on or not is controlled directly by a pulse width modulation (PWM) signal for changing the rotation speed of fan. However, because the design of such a circuit is to directly control the voltage supply Vcc, some signals output by a frequency generator (FG) and a rotation speed detector (RD), bothe of which are electrically connected with the fan, are interfered with the PWM signal. As shown in FIG. 2, under the normal condition, the FG signal representative of the rotation speed of fan has the waveform (a) shown in this figure, but it will become as the waveform (c) when it is interfered with the PWM signal having the waveform (b) so that the actual rotation speed of fan is unable to be detected accurately. Likewise, referring to FIG. 3, the RD signal for detecting the rotation speed of fan is at a relatively low voltage level under the normal condition (shown as the waveform (1)) and will be changed from the relatively low voltage level to the relatively high voltage level only under an abnormal condition. Nevertheless, if the voltage supply of a fan is directly controlled by the PWM signal, the RD signal will become as the waveform (3) under the normal condition due to the interference of the PWM signal (shown as the waveform (2)). Because either the FG signal or the RD output signal is interfered with the PWM signal, the actual rotation speed of fan can not be detected out accurately.

[0003] In addition, the switched interval of the transistor 12 is changed along with the variation of a duty cycle of the PWM signal to control the average current supplied for the fan 11. However, if it is desired to drive the fan, the duty cycle of the PWM signal input into the transistor must be limited within a certain range enough to allow the fan to rotate, especially more than 30%.

SUMMARY OF THE INVENTION

[0004] An object of the present invention is to provide a controlling device for a heat-dissipating system to prevent a signal output by an external device electrically connected with the heat-dissipating system from being interfered with a pulse width modulation (PWM) signal used for controlling the voltage supply of the heat-dissipating system.

[0005] Another object of the present invention is to provide an improved control circuit of pulse width modulation for a direct-current (DC) fan.

[0006] Another yet object of the present invention is to provide an improved control circuit of pulse width modulation for a direct-current (DC) fan, which can enlarge the control ratio of the duty cycle of the PWM signal.

[0007] The controlling device of the present invention includes a signal generator, electrically connected between the heat-dissipating system and a power source supplying a voltage for the heat-dissipating system, for generating a control signal to switch on/off the power source, and a voltage regulator electrically connected between the heat-dissipating system and the power source and connected in parallel with the signal generator for continuously providing the heat-dissipating system with a basic voltage so as to prevent that an output signal of an external device electrically connected with the heat-dissipating system is interfered with the control signal.

[0008] Preferably, the signal generator is a pulse width modulation (PWM) circuit and the control signal is a pulse width modulation (PWM) signal. The duty cycle of the pulse width modulation signal can range from 0% to 100% without any limitation.

[0009] In addition, the controlling device further includes an electronic switch electrically connected between the power source and the heat-dissipating system and connected with the PWM circuit for receiving the pulse width modulation signal and controlling a rotation speed of a fan of the heat-dissipating system corresponding to the duty cycle of the pulse width modulation signal. Preferably, the electronic switch is a transistor.

[0010] In accordance with one aspect of the present invention, the voltage regulator can be a zener diode, a resistor, a voltage supply which supplies a voltage lower than the voltage supplied by the power source, or a circuit which provides an internal circuit in the heat-dissipating system with a basic voltage.

[0011] The external device electrically connected with the heat-dissipating system includes a detector for detecting a rotation speed of a fan in the heat-dissipating system, or a frequency generator for generating a square-wave signal representative of a rotation speed of a fan in the heat-dissipating system.

[0012] The present invention may best be understood through the following description with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a schematic diagram showing a conventional control circuit of pulse width modulation (PWM) for a direct-current (DC) fan;

[0014]FIG. 2 shows the situation that the output signal of the frequency generator electrically connected with the fan is interfered with the PWM signal output by the conventional PWM control circuit;

[0015]FIG. 3 shows the situation that the output signal of the rotation speed detector electrically connected with the fan is interfered with the PWM signal output by the conventional PWM control circuit; and

[0016]FIG. 4 is a schematic diagram showing a preferred embodiment of the controlling device for a heat-dissipating system according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] The present invention will now be described more detailedly with reference to the following embodiments. It is to be noted that the following descriptions of the preferred embodiments of this invention are presented herein for the purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.

[0018] Please refer to FIG. 4 showing a preferred embodiment of the controlling device for a heat-dissipating system according to the present invention, wherein the heat-dissipating system is exemplified by a direct-current (DC) fan 41. The controlling device includes a signal generator, electrically connected between the fan 41 and a voltage supply Vcc supplying a voltage for the fan 41, for generating a control signal for switching on/off the voltage supply; and a voltage regulator 42 electrically connected between the fan 41 and the voltage supply and connected in parallel with the signal generator for continuously providing the fan 41 with a basic voltage so as to prevent that an output signal of an external device electrically connected with the fan 41 is interfered with the control signal. The external device includes a detector for detecting a rotation speed of a fan (indicated by RD), or a frequency generator (indicated by FG) for generating a square-wave signal representative of a rotation speed of the fan. By the design of such a controlling device, the RD signal output by the detector can be kept at a low voltage level under a normal condition and will be changed to a high voltage level only in an abnormal condition. Therefore, the actual rotation speed of fan can be precisely detected without being affected by the control signal. Likewise, corresponding to the actual rotation speed of fan, the frequency generator will generate a square-wave signal with a specific frequency which will not be influenced by the control signal.

[0019] Preferably, the signal generator is a pulse width modulation (PWM) circuit 43 which is electrically connected between the voltage supply Vcc and the fan 41 through an electronic switch or a transistor 44 to generate a pulse width modulation (PWM) signal (as a control signal). The PWM circuit can change the duty cycle of the PWM signal according to the square-wave signal generated by the frequency generator so as to further control the rotation speed of fan.

[0020] The electronic switch or transistor 44 electrically connected between the voltage supply Vcc and the fan and electrically connected with the PWM circuit 43 is used to receive the PWM signal and further control the current flowing through the fan 41. Immediately after receiving the PWM signal, the switched interval of the transistor 44 is changed along with the variation of the duty cycle of the pulse width modulation signal and the average current flowing through the fan 41 is also changed. Therefore, the rotation speed of the fan 41 can be controlled by changing the duty cycle of the pulse width modulation signal. Furthermore, the duty cycle of the PWM signal can be controlled within the range of 0% to 100% rather than limiting the duty cycle in some degree like the prior art.

[0021] According to the present invention, the voltage regulator 42 can be a zener diode, a resistor, a voltage source which supplies a voltage lower than the voltage supplied by the voltage supply Vcc, or a circuit which provides an internal circuit in the fan 41 with a basic voltage. The main function of this voltage regulator 42 is to continuously the most basic voltage for the internal circuit in the fan so that the signal output by the frequency generator or the rotation speed detector will not be affected by the PWM signal, thereby accurately detecting out the actual rotation speed of the fan 41.

[0022] In conclusion, not only can the simplified control circuit for a heat-dissipating system of the present invention prevent a signal output by an external device electrically connected with the heat-dissipating system from being interfered with a pulse width modulation (PWM) signal used for controlling the voltage supply of the heat-dissipating system, but also can achieve the purpose of changing or controlling the rotation speed of DC fan. Moreover, the improved control circuit of pulse width modulation of the present invention can enlarge the control ratio of the duty cycle of the PWM signal.

[0023] While the invention has been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention need not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures. 

What is claimed is:
 1. A controlling device for a heat-dissipating system, comprising: a signal generator electrically connected between said heat-dissipating system and a power source supplying a voltage for said heat-dissipating system, and generating a control signal for switching on/off said power source; and a voltage regulator electrically connected between said heat-dissipating system and said power source and connected in parallel with said signal generator for providing said heat-dissipating system with a basic voltage so as to prevent that an output signal of an external device electrically connected with said heat-dissipating system is interfered with said control signal.
 2. The controlling device according to claim 1 wherein said heat-dissipating system is a direct-current (DC) fan.
 3. The controlling device according to claim 1 wherein said signal generator is a pulse width modulation (PWM) circuit.
 4. The controlling device according to claim 3 further comprising an electronic switch electrically connected between said power source and said heat-dissipating system and connected with said PWM circuit for receiving said pulse width modulation signal and controlling a rotation speed of a fan of said heat-dissipating system corresponding to said duty cycle of said pulse width modulation signal.
 5. The controlling device according to claim 4 wherein said electronic switch is a transistor.
 6. The controlling device according to claim 1 wherein said control signal is a pulse width modulation (PWM) signal.
 7. The controlling device according to claim 6 wherein a duty cycle of said pulse width modulation signal ranges from 0% to 100%.
 8. The controlling device according to claim 1 wherein said voltage regulator is a zener diode.
 9. The controlling device according to claim 1 wherein said voltage regulator is a resistor. 10.The controlling device according to claim 1 wherein said voltage regulator is a voltage source which supplies a voltage lower than said voltage supplied by said power source. 11.The controlling device according to claim 1 wherein said voltage regulator is a circuit which provides an internal circuit in said heat-dissipating system with a basic voltage. 12.The controlling device according to claim 1 wherein said external device electrically connected with said heat-dissipating system includes a detector for detecting a rotation speed of a fan in said heat-dissipating system. 13.The controlling device according to claim 1 wherein said external device electrically connected with said heat-dissipating system includes a frequency generator for generating a square-wave signal representative of a rotation speed of a fan in said heat-dissipating system. 